1. Field of the Invention
The present invention relates to a method for crystal growth utilizing the self-growth-limiting function of bismuth element in the production of a multi-element oxide thin film containing bismuth as a constituent element by vapor phase epitaxy.
2. Description of the Prior Art
As methods for preparing a multi-element oxide thin film by vapor phase epitaxy, sputtering, laser ablation, molecular beam epitaxy, and chemical vapor deposition (CVD) have been developed and have found use. The sputtering method and the laser ablation method use a target with a predetermined chemical composition, while the molecular beam epitaxial method and the CVD method maintain the feed ratios of the constituent elements of a thin film at constant values and grow the crystals of the thin film.
When a multi-element oxide thin film containing bismuth as a constituent element is prepared by a conventional technique, the uptake of bismuth element by the crystals of the thin film is low and sensitively varies with the growth temperature. Thus, the optimum environment for growth is limited to a narrow region, and the bismuth proportion in the thin film often becomes less than in the composition of the desired oxide. Furthermore, a thin film comprising a plurality of crystal phases, being different from the desired crystal phase, may grow, or impurities may precipitate in the thin film. These are major problems with the crystal growth of a multi-element oxide thin film containing bismuth as a constituent element, and pose a serious threat to improving the quality of the thin film. Even if the conditions for the growth temperature or oxidizing gas that can minimize these problems are discovered, they are limited to very narrow ranges. This makes it difficult to reproduce a thin film having the same level of quality.